Chronic diseases are often expressed by episodic worsening of clinical symptoms. Preventive treatment of chronic diseases reduces the overall dosage of required medication and associated side effects, and lowers mortality and morbidity. Generally, preventive treatment should be initiated or intensified as soon as the earliest clinical symptoms are detected, in order to prevent progression and worsening of the clinical episode and to stop and reverse the pathophysiological process. Therefore, the ability to accurately monitor pre-episodic indicators increases the effectiveness of preventive treatment of chronic diseases.
Many chronic diseases cause systemic changes in vital signs, such as breathing and heartbeat patterns, through a variety of physiological mechanisms. For example, common respiratory disorders, such as asthma, chronic obstructive pulmonary disease (COPD), sleep apnea and cystic fibrosis (CF), are direct modifiers of breathing and/or heartbeat patterns. Other chronic diseases, such as diabetes, epilepsy, and certain heart conditions (e.g., congestive heart failure (CHF)), are also known to modify cardiac and breathing activity. In the case of certain heart conditions, such modifications typically occur because of pathophysiologies related to fluid retention and general cardiovascular insufficiency. Other signs such as coughing and sleep restlessness are also known to be of importance in some clinical situations.
Many chronic diseases induce systemic effects on vital signs. For example, some chronic diseases interfere with normal breathing and cardiac processes during wakefulness and sleep, causing abnormal breathing and heartbeat patterns.
Breathing and heartbeat patterns may be modified via various direct and indirect physiological mechanisms, resulting in abnormal patterns related to the cause of modification. Some respiratory diseases, such as asthma, and some heart conditions, such as CHF, are direct breathing modifiers. Other metabolic abnormalities, such as hypoglycemia and other neurological pathologies affecting autonomic nervous system activity, are indirect breathing modifiers.
The following patents and patent application publications, all of which are incorporated herein by reference, may also be of interest:                U.S. Pat. No. 4,657,026 to Tagg;        U.S. Pat. No. 5,235,989 to Zomer;        U.S. Pat. No. 5,540,734 to Zabara;        U.S. Pat. No. 5,743,263 to Baker;        U.S. Pat. No. 5,957,861 to Combs;        U.S. Pat. No. 5,964,720 to Pelz;        U.S. Pat. No. 6,134,970 to Kumakawa;        U.S. Pat. No. 6,375,621 to Sullivan;        U.S. Pat. No. 6,383,142 to Gavriely;        U.S. Pat. No. 6,436,057 to Goldsmith et al.;        U.S. Pat. No. 6,856,141 to Ariav;        U.S. Pat. No. 6,980,679 to Jeung;        U.S. Pat. No. 6,984,207 to Sullivan;        U.S. Pat. No. 6,984,993 to Ariav;        U.S. Pat. No. 7,025,729 to de Chazal;        US Patent Application 2003/0045806 to Brydon;        US Patent Application 2005/0119586 to Coyle et al.;        US Patent Application 2006/0084848 to Mitchnick;        US Patent Application 2007/0156031 to Sullivan;        US Patent Application Publication 2007/0249952 to Rubin et al.; and        US Patent Application Publication 2008/0005838 to Wan Fong et al.        
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The inclusion of the foregoing references in this Background section does not imply that they constitute prior art or analogous art with respect to the invention disclosed herein.